The present invention relates to a device working on the displacement principle for stepping up or transmitting forces and strokes, comprising a displacer on the input side which is actuated by a piezoelectric element and has a relatively larger cross-section, and also a displacer on the output side which has a relatively smaller cross-section, and a displacer working chamber common to the two displacers and filled with a pressure transmission medium which is formed, at least in the region of one displacer, by an elastomer sealingly closing the side on which said displacer is situated in relation to the side on which the other displacer is situated.
A corresponding device is shown in German Offenlegungsschrift 39 16 539 wherein the displacer working chamber between two displacers may be completely filled with an elastomer serving as a pressure transmission medium. At the same time, the elastomer is able to form a leakproof barrier between the displacers.
German Patent Specification 10 13 139 a similar device shows a displacer on the input side which acts on an elastomer enclosed in a cavity and, on its side remote from the displacer on the input side, bounds a liquid chamber, which in turn is connected by a pipe to a hydraulic unit. By appropriate movement of the displacer on the input side, the liquid chamber can be enlarged or reduced in size so that liquid is displaced from the chamber or received by the chamber.
It is also known in principle, as seen in German Patent Specification No. 36 00 140, that superplastic alloys can be used as pressure transmission medium.
Finally, German Patent Specification No. 37 42 241 shows a piezoelectrically actuated control valve for controlling fuel injection in an internal combustion engine. The relatively short stroke of a piezoelectric element is stepped up hydraulically to produce the relatively long stroke of the valve member of the control valve.
An object underlying the present invention is the provision of a constructionally simple way of piezoelectrically actuating the control valve of a fuel injection system.
This object has been achieved according to the present invention with the aid of a device of the type indicated at the outset, in which the displacer on the output side is drivingly coupled to the valve member of a control valve in a fuel injection system of an internal combustion engine, and the elastomer disposed on the displacer on the output side forms a leakproof barrier between a pipe system carrying fuel on the side where the displacer on the output side is disposed and the piezoelectric element, and also forms a fastening for the displacer on the output side.
In the present invention, the elastomer has multiple functions, since, on one hand, it serves as a pressure transmission medium and, on the other hand, it acts as a screen for the piezoelectric element in relation to the fuel system. Consequently, it is possible to produce a construction similar to one for conventional hydraulic force and stroke transmission between a piezoelectric element and the valve member of the control valve; at the same time, however, the comparatively expensive sealing arrangement necessary for hydraulic force and stroke transmission, which have to keep the fuel away from the piezoelectric element in order to avoid breakdowns, are dispensed with. Finally, the elastomer also serves to fasten the displacer on the output side, particularly during its installation.
In connection with further features of the present invention, for example, the usually non-reproducible position of rest of the piezoelectric element can be compensated for hydraulically.